Real Actuator Research Articles

Integrated model control simulations of the electron density profile and the implications of using multiple discrete pellet injectors for control

Pellet injection is regarded as the only realistic actuator for core density control in future reactors such as ITER and DEMO. However, a control strategy that can reliably regulate the plasma close to operational limits using multiple pellet injectors is not yet available. In this paper, we present the first integrated model control simulations where a dedicated model-predictive controller is included in JINTRAC. We show that, when continuous actuators are considered, a simple transport model with a steady-state disturbance rejection paradigm is capable of capturing the particle transport dynamics for multiple transport models and scenarios. This in turn allows the model-predictive controller to deal with the uncertainty and minimize the control error given the limited actuation space. Furthermore, we show that for ITER and DEMO relevant pellet sizes, the discrete, nonlinear dynamics of pellet injection will limit the control performance and jeopardize the constraints if not accounted for by the controller. Hence, we conclude that for high-performance control on future reactors, controllers will have to be developed that explicitly deal with the discrete pellet dynamics.

Observer-Based Boundary Fuzzy Control Design of Nonlinear Parabolic PDE Systems Using Mobile Sensors

This paper studies the boundary fuzzy control problem for nonlinear parabolic partial differential equation (PDE) systems under spatially noncollocated mobile sensors. In a real setup, sensors and actuators can never be placed at the same location, and the noncollocated setting may be beneficial in some application scenarios. The control design is very difficult due to the noncollocated mobile observation, which can be solved by an observer-based technique. At first, a Takagi-Sugeno fuzzy PDE model is devoted to accurately representing the nonlinear parabolic PDE system. Next, we present a state estimation scheme including fuzzy Luenberger-type PDE state observer plus mobile sensor guidance. Then, an observer-based boundary fuzzy controller is posed to render the resulting closedloop system exponentially stable, and the exponential decay rate is increased by the designed mobile sensor guidance laws. At last, two examples verify the proposed method.

Modified reconstruction algorithm for probabilistic inspection of damage based on damaged virtual sensing paths

Ultrasonic guided wave is an effective approach for structural damage detection, among which the reconstruction algorithm for probabilistic inspection of damage (RAPID) is widely used. For the problem that the localization accuracy of traditional RAPID is seriously affected by the damage shape factor β, this paper proposes a modified RAPID based on damaged virtual sensing paths (DVSPs). The DVSP is determined by the time of flight (TOF) or damage index (DI) and is defined as a line of passing damage from a real actuator to a virtual sensor. Using DVSPs instead of real paths for damage localization can effectively avoid the β selection dilemma. Experiments were conducted on an aluminum plate and composite laminates. With the change of β, the average localization error does not exceed 9 mm, and the variation is less than 2 mm, while the error variance of the traditional RAPID is more than 35 mm.

Forward Kinematics Based Prediction for Bending Motion of Soft Pneumatic Actuators with Various Air Chambers

This study proposes a forward kinematic model for soft actuators that utilize pneumatic control to predict their bending motion, which is simulated using Ansys software. Firstly, a bending motion test is conducted with a 2-air chamber actuator to derive an equation that establishes the relationship between the bending angle and input pressure. Next, a serial model for the overall soft actuator is developed using forward kinematics with the DH method. The angle variables in the soft actuator are then replaced with an equation that relates the deformed angle and compressed air. Finally, the proposed serial model is used to predict the bending motion of 4-air and 6-air chamber actuators, and the results are compared to simulations and real experiments. The comparison shows that the proposed model could accurately predict the bending motion of the real actuators within an acceptable tolerance of 10%.

Analysis of ideal models of real nonlocal acoustic and elastic metamaterials

Nonlocal coupling in acoustic and elastic systems has received growing attention for its potential to expand the capabilities of active metamaterials. Previously, we have shown experimentally how nonlocality imposed through action at a distance, where signals from disturbances at one location are used to drive actuators at separate locations, gives rise to unique scattering characteristics, namely highly nonreciprocal transmission. We showed how the mathematical models for these experimental systems were excellent predictors for real system behavior, and as such, represented powerful experimental design tools. However, these models were elaborate, incorporating the characteristics of real sensors and actuators, electronic controllers, and material properties and geometries, consequently obscuring the underlying nonlocal physics responsible for their unique behavior. Here, we present simplified models of these real systems that feature closed form expressions for system scattering characteristics, allowing for the identification of relevant dimensionless quantities and revealing how the interactions of those quantities affect both system performance and stability. We compare and contrast ideal models for both acoustic and elastodynamic nonlocal systems, highlighting how each ideal model is qualitatively representative of its real counterpart, thus providing a pathway to a deeper understanding and further exploration of nonlocality in wave-bearing systems.

A Theoretical Investigation of the Ability of Magnetic Miniature Robots to Exert Forces and Torques for Biomedical Functionalities

Magnetic miniature robots exert forces and torques onto the environment to conduct minimally invasive diagnostic and therapeutic tasks. The orders of magnitude of forces and torques determine what functionalities these robots can achieve. Although some studies have been dispersedly reported, the forces and torques have yet to be systematically investigated within biomedical context from underlying physical principles, leaving their theoretical limits elusive. This work constructs a theoretical framework from governing equations to calculate the forces and torques exerted by magnetic miniature robots in their respective targeted workspace to achieve functionalities. It reports that the existing miniature robots with a maximum characteristic length of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-2}$</tex-math></inline-formula> m can exert a force and a torque up to the order of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> N and 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-2}$</tex-math></inline-formula> Nm, respectively, considering realistic actuation paradigms and constraints. The attainable force and torque magnitudes are on par with the requirements of surgeries at human head (e.g., brain, eyes, and ears surgeries) or within adjacent regions of human skin (e.g., surgeries in the bladder and some blood vessels), as well as the surgeries on small animals. But they are insufficient for operations in deep-buried regions of large animals and human (e.g., implant therapy, biopsy, and tissue removal). Hence, potential strategies to further raise the ceiling of the ranges are examined to extend the functionality catalog and expand the operating scope of these robots.

Intranasal delivery of a synthetic Entamoeba histolytica vaccine containing adjuvant (LecA + GLA-3 M−052 liposomes): In vitro characterization

Amebiasis, a disease caused by the parasite Entamoeba histolytica, is estimated to cause millions of infections and at least 55,000 deaths globally each year. With no vaccine currently available, there is an urgent need for an accessible means of stimulating protective mucosal immunity. The objective of this study was to characterize the nasal spray of a novel amebiasis vaccine candidate from a syringe-based liquid atomization device, the Teleflex MAD Nasal™, in both adult and infant nasal airways.Human ergonomic testing was completed to determine realistic actuation parameters. Spray pattern, plume geometry, and droplet size distribution were measured to evaluate reproducibility of free plume characteristics. The Alberta Idealized Nasal Inlet (AINI) and three realistic infant nasal airways were used to determine the in vitro deposition profile in adult and infant airways, respectively.Collectively, in vitro results demonstrated the feasibility of delivering the vaccine candidate to target sites within the nasal airways. Penetration through the nasal airways that could lead to deposition in the lungs was below the limit of quantification for both adult and infant geometries, indicating a low likelihood of adverse events due to lung exposure. These results support continued investigation of intranasal delivery of the synthetic Entamoeba histolytica vaccine.

Hybrid Circuit Actuator Design for Ship Course Control Experiment

This brief presents a low cost hardware-in-the-loop experimental design for large ship course control with actuator in the form of hybrid circuit, which can effectively capture the essential properties of friction and provide a more realistic environment to perform test. According to the Coulomb plus static friction model formulation, the velocity decision circuit, the absolute value circuit and the friction decision circuit are designed based on the basic circuit components and are validated by a series of simulations, respectively. Besides, the circuit of PID controller and the linear model of steering gear are also added to generate the closed-loop actuator. In addition, the model of the ship and the corresponding PID course controller are realized by the algorithm in the computer. The numerical model and the circuit implementation of realistic actuator can exchange information to establish a hardware-in-the-loop experimental platform. Finally, several experiments are carried out to verify the effectiveness of the proposed low-cost system.

Fracture Toughness and Blocking Force of Temperature-Sensitive PolyNIPAAm and Alginate Hybrid Gels.

In the field of actuator materials, hydrogels that undergo large volume changes in response to external stimuli have been developed for a variety of promising applications. However, most conventional hydrogels are brittle and therefore rupture when they are stretched to moderate strains (~50%). Thus, gels to be used for actuators still require improved mechanical properties and actuation performance. In this study, we synthesized a tough and thermo-sensitive hydrogel with a large actuation force by forming interpenetrating networks between covalently crosslinked poly(N-isopropylacrylamide) and ionically crosslinked alginate. Poly(N-isopropylacrylamide) was used as a thermo-sensitive actuation material, and alginate was found to enhance the mechanical properties of the hydrogels. Due to the enhanced elastic modulus and energy dissipation in the hybrid gel, the toughness was increased by a factor of 60 over that of pure PNIPAAm gel. Further, based on the results showing that the hybrid gel exhibits an actuation force that is seven times higher than that of pure PNIPAAm gel, the hybrid gel is more applicable to real actuators.

Flutter test of rudder with real servo actuator in continuous transonic wind tunnel

Flutter wind tunnel test is an important approach of investigation of transonic flutter characteristics of flight vehicle. Comparing with the blow-down wind tunnel, the long-running and low dynamic pressure capabilities of continuous transonic wind tunnel are very suitable for flutter test. The flutter safety protection and analysis of dynamic signals are developed. The safety protection control software, rapid reduction of Mach number and dynamic pressure, model debris catch screen are integrated, which can provide safety protection of test model and wind tunnel. During the test process, the flutter boundary can be achieved by interpolating the reciprocal of spectrum peak. The flutter tests of rudder are conduct through two methods of step and continuous varying dynamic pressure. It is illustrated that the error of flutter dynamic pressure is relatively small, less than 5% between the two methods. Meanwhile, the feedback effect of the real servo actuator on the flutter characteristics is hard to be obtained via numerical simulation. It is demonstrated that the flutter dynamic pressure has been increased by 10% due to the feedback effect.

Offline Programming Guidance for Swarm Steering of Micro-/Nano Magnetic Particles in a Dynamic Multichannel Vascular Model

Magnetically targeted drug delivery (MTD) systems are used in the treatment of various diseases. However, few studies on the targeting of micro-/nano-sized magnetic particles (MPs) inside multi-bifurcations vessel with fluid flow have appeared. Here, we present a user-interface offline programming guidance (OLPG) scheme that controls MPs within a multi-channel dynamic vascular model. The OLPG scheme can simplify the guidance complexity for MTD and overcome the difficulties in real-time sensing of magnetic nanoparticles (MPs). Calibration between real and virtual environments minimizes OLPG errors due to the aggregation properties of the MPs. A Swarm of Aggregated MPs (SAMPs) can be defined experimentally as the equivalent diameter of a single MP. The joystick position is linearly related to the MP magnetic forces of a real electromagnetic actuator. SAMPs were controlled inside the MTD simulator using the joystick and their control commands can be downloaded to the real controller of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> multi-channel vessel model. We performed both simulations and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> studies in the multi-channel vascular model. A user guided MPs to the desired locations in ∼50% of simulations and ∼49.5% of in vitro studies, in the absence of visual feedback. Also, a realistic 3D blood vessel model was simulated to evaluate the feasibility of the OLPG scheme. Our system has a potential to guide <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> drug delivery.

A 2-DOF Impact Actuator for Haptic Application

The demand for realistic haptic feedback actuators has increased as mobile devices have increased in popularity. However, most current haptic actuators provide limited 1-DOF tactile sensations, such as vibrations. This paper presents a 2-DOF haptic impact actuator that can provide planar directional (e.g., x and y directional) and magnitude tactile cues to a user. We built an impact actuator that was designed to be of such a size that a user can grasp it with one hand. Multiple electromagnets of the actuator drive a permanent magnet to hit the actuator housing, creating an impact. For the control of the impact direction, we assumed the direction of a magnetic field vector at the centre of the actuator would follow that of a reference vector formed by voltage heading into the electromagnet array. The results of magnetic field measurements support our assumption by showing that the trend of the magnetic field vector coincided with that of the reference voltage vector. Furthermore, the measurement of the impact acceleration showed the trend that the impact direction follows the reference voltage vector.

The modeling of a tokamak plasma discharge, from first principles to a flight simulator

A newly developed tool to simulate a tokamak full discharge is presented. The tokamak ‘flight simulator’ Fenix couples the tokamak control system with a fast and reduced plasma model, which is realistic enough to take into account several of the plasma non-linearities. A distinguishing feature of this modeling tool is that it only requires the pulse schedule (PS) as input to the simulator. The output is a virtual realization of the full discharge, whose time traces can then be used to judge if the PS satisfies control/physics goals or needs to be revised. This tool is envisioned for routine use in the control room before each pulse is performed, but can also be used off-line to correct PS in advance, or to develop and validate reduced models, control schemes for future machines like a commercial reactor, simulating realistic actuators and sensors behavior.

The Chain-Link Actuator: Exploiting the Bending Stiffness of McKibben Artificial Muscles to Achieve Larger Contraction Ratios

McKibben artificial muscles, comprised of an expandable bladder wrapped in a double-helix-braided sheath, have the ability to generate forces without restricting motion to occur exclusively along the direction of actuation. This makes them attractive for a variety of applications including soft, wearable, and biomimetic robots. Despite their advantages, the theoretical maximum contraction ratio of McKibben muscles is only 36.3\%, which restricts the range of motion of the systems they actuate. This work introduces a novel ‘chain-link actuator’ that exploits the bending stiffness of McKibben muscles to achieve contraction ratios of more than 50\%. A static model that captures the relationship between pressure, displacement, and force is presented and validated on several real chain-link actuator systems.

Fault-tolerant control of a rotary shape memory alloy actuator using a terminal sliding mode controller

This paper focuses on developing a Fault-tolerant control (FTC) method for a rotary Shape Memory Alloy (SMA) actuator against actuator faults. The SMA actuator uses a pair of SMA wires in the antagonistic configuration for rotating a pulley. A proposed Terminal Sliding Mode Controller (TSMC) is utilized to compensate for the effects of actuator faults and to guarantee acceptable tracking performance in the presence of faults. The developed closed-loop scheme is applied to both a simulated model of the actuator as well as a real actuator in an experimental setup and then, the performance is evaluated and compared with a Proportional (P) controller and a sliding mode controller. It is shown that the proposed scheme works well in both normal and faulty conditions. The experimental results indicate that TSMC has almost no steady-state error while both P and sliding mode controllers have a considerable error (about 20% relative error), in the presence of the actuator faults.

Characterization of Electromagnetic Device by Means of Spice Models

— In this paper, the lumped parameter circuital approach devoted to the simulation of massive, conductive, and ferromagnetic cores including eddy currents and nonlinearity is presented. In the first part of the paper, the circuit analogies devoted to the simulation of magnetic structure coupled with external electrical and eventually mechanical equations are summarised. The two techniques are known in the literature as reluctance-resistance and permeancecapacitance analogies. In particular, it is put in evidence the exploitation of the gyrator component in the modelling of the coupling among magnetic and electrical quantities. The originality of this paper consists in demonstrating for the first time that the rotator-capacitor approach is very suitable for simulations in spice environment and the solution is validated on real applications. Following the circuital approach, the effect of the conductivity and nonlinear magnetic behaviour of the magnetic branches is formalized and introduced in the model. The simulation of the conductivity behaviour, which introduces in massive cores significant eddy current effects, is modelled according to the two possible analogies: the reluctance and the permeance-capacitor model. Under sinusoidal steady-state behaviour, energy aspects related to the two models are then presented and discussed. The nonlinearity is taken into account through the fixed-point technique which is suitable for a lumped circuit representation. The full circuital approach is then adopted for the simulation of the real electromechanical actuator under transient and sinusoidal steady-state behaviour conditions. The simulated result is then compared with numerical finite element and experimental result

Stabilization of port-Hamiltonian systems by nonlinear boundary control in the presence of disturbances

In this paper, we are concerned with the stabilization of linear port-Hamiltonian systems of arbitrary orderN∈ ℕ on a bounded 1-dimensional spatial domain (a,b). In order to achieve stabilization, we couple the system to a dynamic boundary controller, that is, a controller that acts on the system only via the boundary pointsa,bof the spatial domain. We use a nonlinear controller in order to capture the nonlinear behavior that realistic actuators often exhibit and, moreover, we allow the output of the controller to be corrupted by actuator disturbances before it is fed back into the system. What we show here is that the resulting nonlinear closed-loop system is input-to-state stable w.r.t. square-integrable disturbance inputs. In particular, we obtain uniform input-to-state stability for systems of orderN= 1 and a special class of nonlinear controllers, and weak input-to-state stability for systems of arbitrary orderN∈ ℕ and a more general class of nonlinear controllers. Also, in both cases, we obtain convergence to 0 of all solutions ast→∞. Applications are given to vibrating strings and beams.

Majorant-Based Control Methodology for Mechatronic and Transportation Processes

This paper provides a unified approach via majorant systems, which allows one to easily design a family of robust, smooth and effective control laws of proportional - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$h$ </tex-math></inline-formula> order integral - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> order derivative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(PI_{h} D_{k})$ </tex-math></inline-formula> -type for broad classes of uncertain nonlinear multi-input multi-output (MIMO) systems, including mechatronic and transportation processes with ideal or real actuators, subject to bounded disturbances and measurement errors. The proposed control laws are simple to design and implement and are used, acting on a single design parameter, to track a sufficiently smooth but generic reference signal, yielding a tracking error norm less than a prescribed value, with a good transient phase and feasible control signals, despite the presence of disturbances, parametric and structural uncertainties, measurement errors, and in case of real actuators and amplifiers. Moreover, some guidelines to easily design the proposed controllers are given. Finally, the stated unified methodology and various performance comparisons are illustrated and validated in two case studies.

Evolving Fuzzy Model Identification of Nonlinear Wiener-Hammerstein Processes

This paper presents a new approach to neuro-fuzzy model identification based on a filtered recursive least squares method combined with an incrementally evolving Gaussian clustering method. The proposed identification algorithm generates the model on the fly and requires few user-defined parameters, which is one of the main advantages compared to other methods. The partitioning of the input-output data space depends on the chosen criteria and thresholds and depends only on the operating point of the model. As an example, the Wiener-Hammerstein type of a dynamic process was identified to show the potential of the proposed method in identifying nonlinear dynamic models. The Wiener-Hammerstein structure was used because a variety of processes can be modeled with this type of structure. Moreover, we tested the same identification concept on a real heat exchanger plant with strong nonlinear behavior. In addition, the limitations of the real sensors and actuators represent a serious challenge to the identification procedure. Both experiments, on a simulated Wiener-Hammerstein model and on a real plant, have shown that the proposed new neuro-fuzzy model identification with the new merging concept is very easy to implement, can perform all necessary calculations online, and can generate meaningful models.

Next-Generation Prosthetic Hand: from Biomimetic to Biorealistic.

Integrating a prosthetic hand to amputees with seamless neural compatibility presents a grand challenge to neuroscientists and neural engineers for more than half century. Mimicking anatomical structure or appearance of human hand does not lead to improved neural connectivity to the sensorimotor system of amputees. The functions of modern prosthetic hands do not match the dexterity of human hand due primarily to lack of sensory awareness and compliant actuation. Lately, progress in restoring sensory feedback has marked a significant step forward in improving neural continuity of sensory information from prosthetic hands to amputees. However, little effort has been made to replicate the compliant property of biological muscle when actuating prosthetic hands. Furthermore, a full-fledged biorealistic approach to designing prosthetic hands has not been contemplated in neuroprosthetic research. In this perspective article, we advance a novel view that a prosthetic hand can be integrated harmoniously with amputees only if neural compatibility to the sensorimotor system is achieved. Our ongoing research supports that the next-generation prosthetic hand must incorporate biologically realistic actuation, sensing, and reflex functions in order to fully attain neural compatibility.